The present disclosure relates to a process for producing compatibilized blends of a first polymer and a second polymer to form a variety of articles having improved properties. More specifically, the disclosure relates to a process for manufacturing blends/compositions of a first relatively flexible polymer and a second relatively rigid polymer, as well as articles formed from such compatibilized polymer blends/compositions.
Compatibilized blends of relatively flexible hydrophobic polymers, such as polyolefins (PO), and relatively hydrophilic rigid polymers, such as engineering thermoplastic (ET) resins, have been made. However, due to the incompatible nature of the polyolefins and the engineering thermoplastic resins, and to the methods that have been used to form the blends, the products made therefrom have not exhibited optimal performance. The blends often exhibit large domains of one discontinuous phase dispersed within a continuous phase. In most cases, the discontinuous phase is made up of the minor component of the blend, and the continuous phase is made up of the major component of the blend.
Conventional methods of obtaining a compatibilized blend also require a multiple step process, wherein in a first apparatus, a polyolefin or other polymer is functionalized to form a compatibilizer, the compatibilizer is isolated, e.g. as pellets or powder, and the compatibilizer is subsequently mixed with the engineering thermoplastic in a second mixing apparatus. The product made from mixing the compatibilizer with the engineering thermoplastic resin is then isolated, e.g. formed as pellets, and subsequently used to form final, end-use articles or products. This plurality of steps is labor intensive, consumes excessive amounts of energy, and causes undesirable degradation of the polymer blend in the subsequent remelting and product formation steps.
Moreover, attempts to provide the engineering thermoplastic downstream in the same machine that is producing the compatibilizer have failed. This is generally due to poor melting of the solid engineering thermoplastic in the molten compatibilizer. The reason for this concerns differences in the melting temperatures. While most polyolefins melt in the range of 50 to 165° C., typical engineering thermoplastic melt in the range of 200-300° C. (Polyamide 6, Polyamide 66, polyethyleneterephthalate (PET), etc.).
For example, in conventional methods, a compatibilizer may be formed “in-house” or purchased from a specialty manufacturer. This compatibilizer is then mixed with an appropriate combination of solid polyolefin and engineering thermoplastic (in the form of pellets, flakes, granules or powder) and melt kneaded (usually in an the extruder or co-kneader) to yield a product, e.g. pellets of the compatibilized blend. Usually, due to differences in melting temperature, the fraction of the engineering thermoplastic polymer is greater than the fraction of the lower melting polymer, in order to enable enough friction between the extruder screw and barrel during melting phase. Due to these limitations, typical compatibilized blends comprise about 5-30% w/w of the lower melting temperature polymer. The pellets are then subsequently provided to another machine to form the final, end-use product. The compatibilizer, whether purchased from the specialty manufacturer, or formed in a separate “in-house” process, is expensive. Moreover, the energy that is invested to melt and graft the monomers to form the compatibilizer is lost during subsequent cooling and pelletizing steps. The need to remelt the compatibilized blend in the process of forming the final, end-use product results in a waste of about 30-60 USD($)/ton in lost energy and also results in degradation of the polymer blend.
Another deficiency of the present technologies of forming alloys (blends that have useful physical properties) of polyolefins or other low melting polymers (styrenic for example) with engineering thermoplastics with higher strength, stiffness and melting point (Polyamide 6, Polyamide 66, polyethyleneterephthalate (PET), etc.) is a limitation derived from the different melting temperatures: since the polyolefin melts first, the engineering thermoplastics are not melted well if a blend of dry pellets or powders or flakes of both is fed to an extruder or similar melt kneader. The reason for that is once the lower melting temperature polymer is melted, the molten material lubricates the pellets of the higher melting point polymer and avoids the essential friction of the pellets with the extruder barrel. Due to this, alloys typically comprise more than 60% engineering thermoplastics and less than 40% polyolefin (for example Orgalloy™ by Arkema). In order to manufacture alloys comprising less than 60% and more preferred less than 40% engineering thermoplastics, further remelting and mixing steps are required. Consequently, the steps then consist of making the compatibilizer, mixing solid compatibilizer with 60% or more engineering thermoplastics and 40% or less polyolefin and melt kneading to form solid alloy comprising 60% or more engineering thermoplastics. This solid alloy is then blended with polyolefin pellets or powder or flakes, fed to an extruder or alike, remelted and melt kneaded to form solid alloy comprising less than 60% engineering thermoplastic.
Consequently, there is a need to provide for more efficient processes for producing compatibilized polymer blends which, among other things, save energy, are less costly, enable production of alloys comprising less than 60% engineering thermoplastic in at most two melt kneading steps and produce less degradation of the product through excessive reprocessing.